Abstract

Structural and optical properties of antimony-containing sodium borate glasses were studied and their ultrafast third-order nonlinear optical (NLO) properties have been evaluated using Z-scan measurements with femtosecond (fs) pulses (?150 fs, 80 MHz) at 750, 800, and 880 nm wavelengths. Glasses in the (mol ) 20Na 2 O-(80 - x)B 2 O 3 -xSb 2 O 3 (where x = 0, 10, 20, and 30) system have been fabricated via melt quench technique. The structural modifications were analyzed using the Raman and magic angle spinning (MAS)-nuclear magnetic resonance (NMR) ( 11 B MAS-NMR and 23 Na MAS-NMR) techniques. The optical absorption spectra revealed that the absorption edge was red-shifted, suggesting the decrease in band gap energy with increase of antimony content in the glasses. Raman scattering results revealed that the boroxol rings are depressed with the incorporation of Sb 2 O 3 for replacing B 2 O 3 . 11 B MAS-NMR results showed a progressive increase of B 4 units at the expense of B 3 units. The Raman and 11 B MAS-NMR results support the formation of Sb 5+ ions due to oxidation of Sb 3+ that played the role of charge compensation. 23 Na MAS-NMR spectra revealed a decreasing trend in the average of bond lengths of Na-O with increasing Sb 2 O 3 contents. This suggested that sodium changed its role from charge compensator to modifier cation. The antimony-containing glasses demonstrated a reverse saturable absorption in open-aperture Z-scan mode due to two-photon absorption, while closed-aperture Z-scan signatures depicted positive nonlinear refraction due to self-focusing effect. The NLO coefficients were found to increase with Sb 2 O 3 due to the increased nonbridging oxygens and also due to the hyperpolarizability of Sb 3+ and Sb 5+ ions. The observed NLO data clearly suggest that the investigated glasses are beneficial for optical limiting applications.